This invention relates to the preparation of test samples for automatic analysis in a sample analysis system and more particularly to a novel apparatus and method for diluting a test sample before it is combined with a reagent in a sample analysis system.
In known automatic sampling systems, such as shown in U.S. Pat. No. 5,268,147, test samples of blood or serum are permitted to react with one or more reagents to produce measurable test results that are the basis for an analytical determination of blood characteristics. Known sampling systems often include a pipette or sampling probe to aspirate a predetermined volume of test sample from a container such as a tube or cuvette. The aspirated test sample is usually mixed with a predetermined volume of diluent before the test sample is added to a reagent. Dilution of the test sample helps control a test reaction when the test sample is combined with a reagent.
One known system for diluting a fluid sample, indicated as prior art in FIGS. 1-3, includes an aspiration probe with two continuous communicable interior sections of different diametrical magnitude. A first interior section of the aspiration probe is proximate an inlet opening, and a second interior section of larger diametrical magnitude is located beyond the first section. Both interior sections of the probe are generally disposed along a vertical axis.
Predetermined amounts of fluid sample and diluent are sequentially aspirated into the first interior section, as detailed in U.S. Pat. No. 5,773,305. The fluid sample and diluent are then drawn further into the probe from the first interior section to the second interior section.
The fluid sample and diluent, when located in the second interior section, are moved back and forth along a substantially vertical axis a predetermined number of times by alternate vacuum and pressure forces. Repeated back and forth movement of the fluid sample and diluent in the second interior section of the probe provides substantially uniform mixing or dilution of the fluid sample.
In many instances an oil coating is provided along the inside surface of the probe and the mixing chamber to facilitate flow and reduce carryover of sample or diluent to a next use of the device. Applicants have found that an oil filled aspiration line and mixing chamber wherein the oil can be withdrawn in the hydraulic line by a pump and later reintroduced into the hydraulic line during dispensation of a diluted test sample serves to minimize carryover.
It is thus desirable to provide a method and apparatus for diluting a test sample and diluent which minimizes carryover of sample or diluent to a next use of an aspiration device.